You don't need a 1600x over a 1600 because they are identical. The only difference is the base clock speeds which don't matter once you overclock past the boost speeds. So just overclocking to 4Ghz makes them identical so why pay more? (4Ghz is easily done with the stock cooler but I gave you an AiO for better temps and higher overclocking)
As for the trident z that superninja suggested I don't personally agree with that choice. Unless you care enough about RGB the price to performance ratio isn't as good as the G.Skill memory I provided. Also, the motherboard change was to give you everything you need in the motherboard but at a better price.
The reason for higher speed RAM is that Ryzen loves fast RAM. The faster, the better and the higher you can overclock (provided you have adequate cooling to go along with it)
That should hopefully answer your initial questions. The reason for me choosing the Meshify C is because it's a better case than the eclipse in my opinion. Just look up review of it on YouTube. It's on sale right now for $80 (which is $10 off) so it's no different than the eclipse in price right now. But if you want to get the eclipse that's up to you. These lists are more for guidance in your purchases rather than literal "you can only buy this and choosing anything else is wrong" kind of thing. It's to give you an idea of what you can actually go for in choosing parts and to show how you can save money or pay the same but get better.
I checked the list I posted and noticed some stuff wasn't right with the links so I've updated it.